Absorbent composites suitable for use in disposable absorbent garments such as diapers, adult incontinent products, and the like, are known. Such absorbent composites are described, for example, in U.S. Pat. No. 4,699,619 issued Oct. 13, 1987, to Bernardin; U.S. Pat. No. 4,798,603 issued Jan. 17, 1989, to Meyer et al.; U.S. Pat. No. 4,834,735 issued May 30, 1989, to Alemany et al.; U.S. Pat. No. 5,147,343 issued Sep. 15, 1992, to Kellenberger; and U.S. Pat. No. 5,149,335 issued Sep. 22, 1992, to Kellenberger et al.
Generally, such absorbent composites comprise a means of containing a high-absorbency material and a high-absorbency material. Suitable means for containing the high-absorbency material include fibrous matrixes, such as those formed from air-laid cellulosic fibers or a coform material comprising cellulosic fibers and meltblown polyolefin fibers. A wide variety of high-absorbency materials (also known as superabsorbent materials) are known to those skilled in the art. See, for example, U.S. Pat. No. 4,076,663 issued Feb. 28, 1978, to Masuda et al.; U.S. Pat. No. 4,286,082 issued Aug. 25, 1981, to Tsubakimoto et al.; U.S. Pat. No. 4,062,817 issued Dec. 13, 1977, to Westerman; and U.S. Pat. No. 4,340,706 issued Jul. 20, 1982, to Obayashi et al.
Many known absorbent composites comprising a high-absorbency material employ the high-absorbency material in relatively low concentrations. That is, many of the absorbent composites comprise airlaid. cellulosic fibers and less than about 20 weight percent of a high-absorbency material. This is due to several factors.
Many high-absorbency materials are unable to absorb a liquid at the rate at which the liquid is applied to the absorbent composites during use. Accordingly, a relatively high concentration of fibrous material is desirable to temporarily hold the liquid until the high-absorbency material can absorb it. Further, the fibers serve to separate the particles of high-absorbency material so that gel-blocking does not occur. Gel-blocking refers to the situation wherein particles of high-absorbency material deform during swelling and block the interstitial spaces between the particles, or between the particles and the fibers, thus preventing the flow of liquid through the interstitial spaces.
U.S. Pat. No. 5,147,343 issued Sep. 15, 1992, to Kellenberger describes an absorbent composite adapted to avoid the problem of gel-blocking. U.S. Pat. No. 5,147,343 describes the use of a superabsorbent material which can absorb at least 27 milliliters of a 0.9 weight percent aqueous sodium chloride solution per gram of superabsorbent material while the superabsorbent is under a restraining pressure of at least 21,000 dynes per square centimeter. When the superabsorbent material is in the form of discrete particles, at least about 50 percent by weight of the superabsorbent material has a size greater than the median pore size of the porous fiber matrix when wet. The described absorbent composites are said to contain up to about 90 weight percent of a superabsorbent material.
The presence of a relatively low concentration of high-absorbency material and a relatively greater concentration of fibrous materials has resulted in the production of absorbent composites which tend to be relatively thick. In some instances, the use of a relatively thick absorbent composite in a disposable absorbent garment is acceptable. However, in recent years it has become increasingly desirable to produce absorbent composites which are thin compared to the more traditional absorbent composites but which still possess the same absorbent capacity. The desire to produce relatively thin absorbent composites has resulted in the desire to incorporate ever-increasing amounts of high-absorbency material into the absorbent composites. This is because the absorbent capacity of such high-absorbency materials is generally many times greater than the absorbent capacity of fibrous materials. For example, a fibrous matrix of wood pulp fluff can absorb about 7-9 grams of a liquid, (such as 0.9 weight percent saline) per gram of wood pulp fluff, while the high-absorbency materials. can absorb at least about 15, preferably at least about 20, and often at least about 25 grams of liquid, such as 0.9 weight percent saline, per gram of the high-absorbency material.
U.S. Pat. No. 5,149,335 issued Sep. 22, 1992, to Kellenberger et al. is directed to an absorbent structure containing a relatively high concentration of superabsorbent material. Specifically, U.S. Pat. No. 5,149,335 describes the use of a superabsorbent material having certain absorbent characteristics when it is desired to employ the superabsorbent material at relatively high concentrations. Specifically, the superabsorbent material is described as having a 5-minute Absorbency Under Load value of at least about 15 grams per gram and a free-swell rate of less than about 60 seconds.
While absorbent composites containing a relatively high concentration of high-absorbency material are known, and are generally acceptable in use, it is desired to more particularly define absorbent composites containing a relatively high concentration of a high-absorbency material and those high-absorbency materials which are well suited for use in absorbent composites comprising a relatively high concentration of the high-absorbency material.
The present invention relates to a method of testing superabsorbent materials for thier suitability for use in absorbent composites to be included in disposable absorbent garments, the absorbent composites comprising from about 30 to about 100 weight percent of superabsorbent materials, the method comprising the steps of
(a) determining the absorbency under load characteristics of the superabsorbent materials at restraining forces of 0.01, 0.29, 0.57, and 0.90 pounds per square inch,
(b) determining the total of the absorbency under load characteristics at each said restraining force for each superabsorbent material, and
(c) choosing as suitable a superabsorbent material for which the total of said absorbency under load characteristics is at least about 110.
It is preferred that a superabsorbent material is selected for which the total of said absorbency under load characteristics is at least about 120, and more preferred that a superabsorbent material is selected for which the total of said absorbency under load characteristics is at least about 140.
It is also preferred that a superabsorbent material is selected which has a 16-hour extractables level of less than about 13 weight percent, particularly of less than about 10 weight percent, more particularly of less than about 7 percent, and even more particularly of less than about 3 weight percent.